Structural domains comprising this superfamily share the structure of the bacterial phosphonate metabolism protein PhnH, an essential component of the C-P lyase core complex formed through the interaction with other Phn proteins (G, I and J). This core complex is involved in the C-P lyase pathway that converts phosphonate into 5-phosphoribosyl-alpha-1-diphosphate (PRPP) and is activated upon phosphate starvation in many bacterial species including Escherichia coli. In E. coli, the 14-cistron phn operon is required for phosphonate uptake and utilisation and encodes an ATP-binding cassette transporter (PhnC, PhnD, and PhnE), a regulatory protein (PhnF) and components required for enzymatic conversion of phosphonate into PRPP (PhnGHIJKLMNOP).

The C-P lyase core complex harbours two key activities of this pathway; coupling of the phosphonate to ATP (PhnG, PhnH, and PhnI) and C-P bond cleavage (PhnJ). PhnH is the only component of the C-P lyase core complex that has been structurally characterised and displays a fold related to the pyridoxal 5'-phosphate-dependent transferases. It forms a homodimer when expressed independently, but its role within the complex is unclear PMID:26280334 PMID:17993513.